Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!usc!snorkelwacker.mit.edu!hsdndev!cmcl2!adm!smoke!gwyn
From: gwyn@smoke.brl.mil (Doug Gwyn)
Newsgroups: comp.lang.c
Subject: Re: Simple atof() question
Message-ID: <15522@smoke.brl.mil>
Date: 20 Mar 91 21:19:29 GMT
References: <1214@caslon.cs.arizona.edu>
Organization: U.S. Army Ballistic Research Laboratory, APG, MD.
Lines: 19

In article <1214@caslon.cs.arizona.edu> armstron@cs.arizona.edu (Jim Armstrong) writes:
>How can I get atof() to return a float instead of a double? 

You can't; it always returns type "double".

>When I run this simple program I get n = 37.549999 instead of
>n = 37.55.  What am I doing wrong?

That's a different question.  There's nothing particularly wrong with
your program, other than failing to return a value from main().  Note
that the float argument to printf() is promoted to a double, but that's
not a problem.

I think your real problem is that you think that the value 37.55 can
be represented exactly in a binary floating-point representation.
Somewhere along the way, probably within atof(), you're picking up a
small amount of "dirt" in the last bit or so of the internal
representation.  This is usual for floating-point; you should learn
from this to not expect exactness when floating-point is involved.